Tacan antenna system

ABSTRACT

The nulls and lobes of a Tacan antenna horizontal and/or vertical radiation patterns due to unwanted reflections are reduced by employing two or more Tacan antennas disposed in a predetermined horizontal and/or vertical spaced relation having each of their radiation patterns rotated synchronously and in phase. In one embodiment, complete redundancy of transmitter and antenna is provided by having a different transmitter coupled to a different one of the two or more antennas timed to sequentially excite the two or more antennas with a Tacan signal. In another embodiment, one transmitter is sequentially coupled to each of the two or more antennas for sequential excitation thereof by a Tacan signal.

[ 51 July 25,1972

[54] TACAN ANTENNA SYSTEM Sven l-I. Dodlngton, Mountain Lakes, NJ.

International Telephone and Telegraph Corporation, Nutley, NJ.

[22] Filed: Aug. 14, 1970 [21] Appl.No.: 63,877

[72] Inventor:

[73] Assignee:

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Richard E. Berger Attorney-C. Cornell Remsen, Jr., Walter J. Baum, Paul W. Hemminger, Charles L. Johnson, Jr., Philip M. Bolton, Isidore Togut, Edward Goldberg and Menotti J. Lombardi, Jr.

[57] ABSTRACT The nulls and lobes of a Tacan antenna horizontal and/or ver tical radiation patterns 'due to unwanted reflections are reduced by employing two or more Tacan antennas disposed [52] US. Cl. ..343/l06 R, 325/154, 343/100 CS [51] Int. Cl ..G0ls 1/46 m a Predetermmed homomal and/or Vemcal Spaced relanon 53] n w of Search "343/106 R 100 325/154 having each of their radiation patterns rotated synchronously 325/65 and in phase. In one embodiment, complete redundancy of transmitter and antenna is provided by having a different 56] References cued transmitter coupled to a different one of the two or more antennas timed to sequentially excite the two or more antennas UNITED STATES PATENTS with a Tacan signal. In another embodiment, one transmitter is sequentially coupled to each of the two or more antennas 2,747,181 5/1956 Granqvist ..343/l06 R f sequential excitation thereef by a Tacan SignaL 3,036,30l 5/1962 Wiesner ..343/l00 CS 10 Claims, 5 Drawing Figures '3 l a 5 1* v frf i 7 7 TACAN TA CA N ARRANCIMf/Jf mamw/rrm rRAA/sM/rrm To R0 r4 r5 0 i RADIATION PATTERNS TACA/V SYIVCRONOl/JLY r TRANSMITTER AND m PHASE 15 3 I18 TIM/m: SOURC ,4

TACAN ANTENNA SYSTEM BACKGROUND OF THE INVENTION This invention relates to antenna systems and more particularly to a Tacan antenna system.

One of the greatest handicaps of single-site omnidirectional beacons, such as Tacan, is the co-called site-error". This error results from the fact that the vehicle which is trying to determine bearing with respect to the beacon, receives not only the direct, correct signal, but also receives signals which have been reflected from various objects, the most damaging of these reflections are those from objects close to the site of the beacon; hence, the term site-error.

The problem of generating the desired Tacan antenna pattern at all sites and vertical elevations and over the full frequency band continues to tax the best brains that can be applied to this job.

Consider, for example, the vertical null problem. Over flat terrain and at the antenna height used by the FAA (Federal Aviation Agency) the vertical lobe and null structure of the antenna pattern is pronounced. If a reflecting object is now added to the scene, the object may reflect to the aircraft an erroneous bearing derived from the radiation in a lobe, while the aircraft is simultaneously receiving the correct beating from a null. Thus, despite the relatively poor reflectivity of the reflecting object, the sum of these two signals may well produce a very substantial bearing error.

To reduce this effect, strenuous efforts have been made in the past to design antennas which have uptilt. These antennas are, first, made to have as much vertical directivity as practical, and then, second, this directivity is projected upwards, above the horizon, so that less energy is reflected from the ground and the vertical nulls are less deep. This solution, is at best, a compromise, since it is difficult to maintain this performance at all frequencies, and the power on the horizon is necessarily decreased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a Tacan antenna system capable of reducing site error.

Another object of the present invention is to provide a Tacan antenna system that does not require specially designed antennas having uptilt.

' Still another object of the present invention is to provide a Tacan antenna system employing diversity like techniques to reduce the null and lobe structures of both the horizontal and vertical radiation patterns of the Tacan antennas.

A feature of the present invention is the provision of a Tacan antenna system comprising a plurality of Tacan antennas disposed in a predetermined spaced relation, each of the plurality of Tacan antennas having a Tacan radiation pattern including nulls and lobes; first means coupled to each of the plurality of Tacan antennas to rotate the radiation pattern of each of the plurality of Tacan antennas synchronously and inphase; and second means coupled to each of the plurality of Tacan antennas to excite each of the Tacan antennas with a Tacan signal; the predetermined spaced relation between the plurality of Tacan antennas being emperically selected to reduce the nulls and lobes in a composite radiation pattern resulting from a combination of the radiation pattern from each of the plurality of Tacan antennas.

BRIEF DESCRIPTION OF THE DRAWING The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of a Tacan antenna system and the electrical and/or mechanical components associated therewith to provide the null reduction in accordance with the principles of the present invention;

FIG. 2 is a curve illustrating the reception of Tacan signals from the antenna system of FIG. 1;

FIG. 3 illustrates the vertical radiation patterns generated by the plurality of antennas of FIG. 1 and the composite radiation pattern resulting therefrom;

FIG. 4 illustrates diagrammatically another embodiment of the Tacan antenna system in accordance with the principles of the present invention; and

FIG. 5 illustrates still another embodiment of the Tacan antenna system in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is illustrated therein one embodiment of the Tacan antenna system in accordance with the principles of the present invention to compensate for nulls and lobes that are introduced by unwanted reflections in the radiation pattern of a single Tacan antenna, such as by an object I, in the form of a tree, at the antenna site. To provide a reduction in the null and lobe structure of the vertical radiation pattern, it is proposed, in accordance with the principles of this invention, to provide a plurality of Tacan antennas 2 and 3 disposed in a vertical spaced relation as illustrated in FIG. 1 with the antenna patterns of these antennas 2 and 3 being rotated synchronously and inphase by arrangement 4.

Arrangement 4 may be a pair of synchronized synchronous motors to drive the antenna structure of antennas 2 and 3, or it may be any known arrangement to electronically rotate the antenna patterns to cause the radiation patterns of antennas 2 and 3 to rotate synchronously and inphase.

In addition, it is proposed that a Tacan signal composed of pairs of pulses, which are amplitude modulated by antenna rotation to provide the bearing information, is provided from Tacan transmitter 5 which through means of electronic switch 6, controlled by the timing source 7, sequentially excites antennas 2 and 3 so as to provide interleaved pulse pairs in each of these antennas whereby the RF pulse pairs are not added, but yet the modulation envelope of these interleaved pulse pairs are added, such as illustrated in FIG. 2 wherein the vertical dash lines 7 indicate pulse pairs from one of the antennas 2 and 3 and the solid vertical lines 8 indicate the pulse pairs from the other of the antennas 2 and 3 with the envelope of the stronger being indicated by line 9.

In this arrangement, with the vertical distance between antennas 2 and 3 being such that up to a considerable angle above the horizon, the aircraft is always in the lobe of one of the antennas 2 and 3 and in the null of the others of antennas 2 and 3. These radiation patterns are illustrated in FIG. 3 wherein the dot-dash lobes 10 are the vertical radiation patterns from one of the antennas 2 and 3 and the dashed lobes 111 are the vertical radiation patterns from the other of the antennas 2 and 3. It will be noted that there is a considerable null at point 10a in the dot-dash radiation pattern which is filled in by the dashed radiation pattern of the other of the vertically stacked antennas resulting in a composite radiation pattern represented by the solid line 12.

Alternatively, it would be possible to provide both redundant Tacan transmitters and redundant Tacan antennas which would have the additional advantage of still being able to provide Tacan bearing information of reduced quality even if one of the transmitters and/or antennas should malfunction. This would be accomplished by deactivating switch 6 and moving switches 13,14,15 and 16 to their position other than the one shown in FIG. 1. In this way, the Tacan transmitters 14 and 15 are coupled to their associated one of antennas 2 and 3 and through the control of the timing source 7, antennas 2 and 3 are sequentially excited so as to provide the desired interleaved pulse pairs from Tacna antennas 2 and 3 as shown in FIG. 2.

As can be seen from the above, advantage has been taken in the Tacan arrangement of exploiting the pulse characteristic thereof. That is, that bearing information is produced by amplitude modulation of low duty cycle In the standard system, each 15 cycle sine wave is defined by the amplitude of some 200 pairs of pulses, with a duty cycle of about 2 percent. It is, therefore, possible to provide an antenna system wherein each of the antennas is fed by a different pulse or group of pulses, the antennas not being simultaneously energized, and, therefore, not producing unwanted radiation patterns.

The foregoing description of FIGS. s 1, 2 and 3 have been concerned primarily with the reduction of nulls and lobes in the vertical radiation pattern. This principle can just as well be applied to the horizontal radiation pattern where lobes and nulls may also be caused by unwanted reflections from an object 1 as shown in FIG. 4. To correct for unwanted nulls and lobes in the horizontal radiation pattern, that is, to reduce the reception of erroneous bearing information, it is proposed that three or more Tacan antennas 19, 20 and 21 be disposed in a horizontally spaced relation having a given geometric configuration which is triangular as illustrated in FIG. 4, such that the nulls and lobes of the horizontal radiation patterns overlap so as to reduce the unwanted deep nulls and lobes of a single radiation pattern that would result from interference from a reflecting object 1. Although the present invention may employ multilobe Tacan antennas, simplicity of the antenna system of the present invention is enhanced by employing a plurality of small beacons with single lobe antennas whose bearing outputs at 15 cycles is receivable by all modern Tacan air borne sets. Typical applications are on board aircraft, for rendezvous and station keeping and on the ground for support of tactical operations. The single lobe antennas, of course, do not provide as much site freedom as the multilobe designs. However, a plurality of single lobe antennas might well provide a substantial improvement and, due to each having its own transmitter, would permit a greater total duty cycle as well as reliability improvement due to redundancy.

It should be kept in mind that the improvement in horizontal and vertical radiation pattern through the employment of diversity techniques as described hereinabove with respect to FIGS. 1 and 4 is not limited to two or three Tacan antennas, but may be provided by up to or more Tacan antennas with their associated transmitters, each of which are appropriately timed to provide their pulse pairs or groups of pulse pairs in an interleaved arrangement, by a timing source similar to timing source 7. The advantage of this system over the system of a single Tacan transmitter and a switching arrangement is the elimination of the switching arrangement and the redundancy afforded by each antenna having its own transmitter.

It will be obvious due to the foregoing discussion that it may be desired to provide simultaneously both reduction of the nulls and lobes in the vertical radiation pattern and the horizontal radiation pattern. This can be provided by employing a plurality of antennas 22 and 23 which are spaced both horizontally and vertically so as to provide due to the combination of their individual radiation patterns a composite radiation pattern having reduced nulls and lobes in both their horizontal and vertical radiation patterns.

It should be pointed out that the horizontal and/or vertical spacing of the antenna arrangements of FIGS. 1, 4 and 5 will depend upon the specific site of the Tacan beacon and, therefore, the spacing both horizontally and/or vertically is determined empirically, since the reflecting objects or object at each site will vary from site to site and, accordingly, the Tacan antenna system must be designed for the particular site in question.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim: 1. A Tacan antenna system comprising: a plurality of Tacan antennas disposed in a predetermined spaced relation, each of said plurality of Tacan antennas having a Tacan radiation pattern including nulls and lobes; first means coupled to each of said plurality of Tacan antennas to rotate said radiation pattern of each of said plurality of Tacan antennas synchronously and inphase; and second means coupled to each of said plurality of Tacan antennas to excite each of said Tacan antennas with a Tacan signal; said predetermined spaced relation being empirically selected to reduce said nulls and lobes in a composite radiation pattern resulting from the combination of said radiation pattern from each of said plurality of Tacan antennas. 2. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined vertically spaced relation. 3. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontally spaced relation. 4. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal spaced relation and in a given geometric configuration. 5. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal and vertical spaced relation. 6. A system according to claim 1, wherein said second means includes a plurality of sources of said Tacan signal, each of said sources coupled to a different one of said plurality of Tacan antennas, said sources sequentially exciting said plurality of Tacan antennas with said Tacan signal. 7. A system according to claim 1, wherein said second means includes a single source of said Tacan signal, and third means to sequentially couple said source to each of said plurality of Tacan antennas to sequentially excite each of said plurality of Tacan antennas with said Tacan signal. 8. A system according to claim 7, wherein said Tacan signal includes a radio frequency pulse signal amplitude modulated by Tacan reference signals; and said third means causes each of said plurality of Tacan antennas to radiate said radio frequency pulse signal in a sequential relation so that said radio frequency pulse signals do not add while said amplitude modulation envelope does add to maintain said Tacan reference signals. 9. A system according to claim 7, wherein said plurality of Tacan antennas are disposed in a predetermined vertically spaced relation. 10. A system according to claim 7, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal spaced relation and in a given geometric configuration. 

1. A Tacan antenna system comprising: a plurality of Tacan antennas disposed in a predetermined spaced relation, each of said plurality of Tacan antennas having a Tacan radiation pattern including nulls and lobes; first means coupled to each of said plurality of Tacan antennas to rotate said radiation pattern of each of said plurality of Tacan antennas synchronously and inphase; and second means coupled to each of said plurality of Tacan antennas to excite each of said Tacan antennas with a Tacan signal; said predetermined spaced relation being empirically selected to reduce said nulls and lobes in a composite radiation pattern resulting from the combination of said radiation pattern from each of said plurality of Tacan antennas.
 2. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined vertically spaced relation.
 3. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontally spaced relation.
 4. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal spaced relation and in a given geometric configuration.
 5. A system according to claim 1, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal and vertical spaced relation.
 6. A system according to claim 1, wherein said second means includes a plurality of sources of said Tacan signal, each of said sources coupled to a different one of said plurality of Tacan antennas, said sources sequentially exciting said plurality of Tacan antennas with said Tacan signal.
 7. A system according to claim 1, wherein said second means includes a single source of said Tacan signal, and third means to sequentially couple said source to each of said plurality of Tacan antennas to sequentially excite each of said plurality of Tacan antennas with said Tacan signal.
 8. A system according to claim 7, wherein said Tacan signal includes a radio frequency pulse signal amplitude modulated by Tacan reference signals; and said third means causes each of said plurality of Tacan antennas to radiate said radio frequency pulse signal in a sequential relation so that said radio frequency pulse signals do not add while said amplitude modulation envelope does add to maintain said Tacan reference signals.
 9. A system according to claim 7, wherein said plurality of Tacan antennas are disposEd in a predetermined vertically spaced relation.
 10. A system according to claim 7, wherein said plurality of Tacan antennas are disposed in a predetermined horizontal spaced relation and in a given geometric configuration. 